Secretory cells from rats pituitaries are studied in vitro to compare their physiology in old and young animals. Production of TSH in response to TRH and production of LH and FSH and their subunits in response to LRH have been measured in order to investigate altered function of pituitary secretory cells. Deficient function of aged pituitary cells in vitro has been found. Castration increases LRH responsiveness of gonadotrophs of aged and young rats to the same extent. Experiments to define the biochemical differences in glycoprotein hormone synthesis in aged pituitary cells are being undertaken as well as experiments to investigate effects of LHRH in vivo pre-treatment on in vitro function of pituitary cells.